Low-Shrinkage UPR

Low-Shrinkage UPR incorporates thermoplastic additives (typically polystyrene or polyvinyl acetate) dissolved in the styrene phase that phase-separate during cure and micro-expand, compensating for the volumetric shrinkage inherent in conventional UPR systems. Standard UPR shrinks 6-10% volumetrically on cure; this formulation reduces shrinkage to 1-3%.

This low shrinkage characteristic dramatically improves dimensional accuracy, reduces warpage and sink marks, and enables the production of Class A surface quality composite panels. The resin is widely used as the resin component in SMC formulations, but is also available as a low-shrinkage hand lay-up grade for precision tooling, jigs, fixtures, and high-quality surface laminates.

Viscosity at 25°C is 400-700 mPa·s, gel time 15-25 minutes at standard MEKP loadings. Flexural strength is 90-110 MPa and tensile modulus 3.5-4.0 GPa. The thermoplastic phase also improves surface quality: final Barcol hardness is 30-40 but surface smoothness approaches Class A standards when used in a closed tool with good surface finish. Post-cure at 70-80°C for 2 hours is recommended for maximum dimensional stability.